Buried deep in the comments...

My new book Armed America (Nelson Current, 2007) answers some of the questions about what arms were in common civilian ownership when the Second Amendment was ratified. I cite ads offering "hand grenadoes" for sale (probably equivalent to a modern pipe bomb in destructiveness), and the 1786 Boston ordinance prohibiting leaving loaded firearms in buildings (as a fire safety measure) that lists not only small arms, but mortars, artillery, and a bunch of other stuff that would qualify as "destructive devices" today. I don't think they included them on the list because they wanted to be complete.

There was privately owned artillery during the Revolutionary period, although I suspect that almost all of it (because of cost and its lack of utility for hunting) was owned by the various militia organizations.

If you look at the National Firearms Act hearings before the House Ways & Means Committee, you can see that even proponents of it, such as the A-G and his assistant, admitted that a complete ban on sale or possession of machine guns was beyond the authority of the federal government, because of the Second Amendment. Background checks for weapons seem unobjectionable from a Constitutional standpoint, as long as they have some reasonable relationship to public safety. But that's more a function of the person, than of the weapon.